We propose to examine the genetic control of synapse formation in the nematode Caenorhabditis elegans at two levels, 1) at the level of gene products involved in synapses, and 2) at the level of genes governing the specificity of synapse formation. At the first level we propose to determine the subunit structure and localization of the four known forms of acetylcholinesterase, in order to determine their relationship to synapse formation. We also propose to explore the nature of a mutant lacking two of these four forms, and we propose to isolate additional mutants affecting other known synaptic components. At the second level we propose to use cell lineage studies and laser microbeam ablation to study synapse formation in a ganglion whose entire normal synaptic circuitry has been established. We also propose to obtain mutants affecting this circuitry, and to examine some pre-existing sensory-defective mutants for synaptic changes.